[7.05] Reconstruction of Facular Brightening from Sunspot Deficit

D.G. Preminger, S.R. Walton (Cal State Northridge)

It is well established that variations in the total solar
irradiance S can be accurately reproduced using a model
based on the competing influences of the darkening due to
sunspots and brightening due to faculae. In order to
reconstruct S before observations of faculae, measurements
of sunspots alone have been used as a proxy for inferring
the facular brightening. In this work, we would like to
improve the inferred facular brightening as well as gain
insight into the time variation of various solar activity
indicators. We make use of the deficit (darkening) due to
sunspots D and the brightness variation attributed to
faculae, as measured either by the excess emission in the
CaIIK line EK or the MgII core-wing ratio. The cross
correlation of D with either facular quantity shows well
defined peaks at zero and negative lags (in the sense that
facular excess lags D). We conclude that dark features
decay into bright features, to some extent, but some bright
features form coincident with the dark features. From the
cross correlation we create a window function which is
convolved with D to obtain a predicted E. Comparison of
the prediction with the actual value of E shows that E
starts rising at the beginning of cycle 23 before its
reconstruction does. It appears that the onset of solar
activity as measured by facular brightening precedes the
rise in our sunspot deficit. Possible causes are under
investigation.

This research was supported by NSF grant ATM-9912132 and
NASA grants NAG5-7191 and NAG5-7778.